Connector element for rigid electrical conduits and method of making the same



A nl 28, 1970 J. E. MATSON 2 CONNECTOR ELEMENT FOR RIGID ELECTRICALCONDUITS AND METHOD OF MAKING THE SAME Filed Dec. 5,1968

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United States Patent O 3,508,428 CONNECTOR ELEMENT FOR RIGID ELECTRICAL'CONDUITS AND METHOD OF MAKING THE SAME James Edward Matson, Galva,Ill., assignor to All-Steel Equipment Inc., a corporation of IllinoisContinuation-impart of application Ser. No. 652,189, July 10, 1967. Thisapplication Dec. 5, 1968, Ser. No. 786,540

Int. Cl. B21d 11/04 US. Cl. 72327 4 Claims ABSTRACT OF THE DISCLOSUREHollow connector elements for rigid electrical conduits are formed withinternal shoulders by displacing metal inwardly from one end of theelement by means of a special swaging or forging tool without the use ofan outer supporting die and without substantially changing the outersize or shape of the element.

This application is a continuation-in-part of application Ser. No.652,189, now abandoned, entitled Connector Element for Rigid ElectricalConduits and Method of Making the Same, filed July 10, 1967.

SUMMARY OF THE INVENTION In making connector elements for rigidelectrical conduits it has been the practice to neck a portion of largerdiameter hollow tubular stock to a small diameter and then thread thenecked portion. This method is relatively expensive.

In accordance with the present invention, metal is squeezed inwardly orswaged from one end portion of the connector element thereby displacingthis metal in the form of an annular shoulder having a smooth flat faceon the side from which metal was displaced. The resulting connectorelement will have a wall portion on the side of the shoulder from whichthe metal was' displaced which is thinner than the remaining wallportion of the connector. The inner surface of the thinner wall portionis smooth as a result of the swaging operation. The shoulder will extendradially inward beyond the inner surface of the thicker portion of theconnector element. The operation is performed in one step with a specialswaging tool or punch and without a retaining die, thus avoiding theproblem of freeing the piece from the die and enabling the operation tobe performed rapid- 1y. The resulting shoulder is a substantiallyperfect annular ring with a smooth top surface and requires no machiningor trimming operation. The operation does not substantially change thesize or shape of the outer wall of the element. A threaded hole is thenformed through the side wall of the connector element to accommodate aset screw and a separate threaded element is fastened to the connectorelement just described by beading the thinner wall end of the connectorelement around an outwardly extending flange on one end of the threadedmember, which flange rests on the smooth face of the shoulder.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a diagrammatic, verticalview of a connector element prior to having a shoulder formed therein inaccordance with the invention.

FIGURE 2 is a cross-section of the element shown in FIGURE 1 taken alongthe line 22.

FIGURE 3 is a vertical cross-sectional view of a connector elementshowing the manner in which the internal shoulder is formed.

FIGURE 4 is a vertical cross-sectional view of the connector elementshown in FIGURE 3 after the mandrel and swaging tool have been removed.

FIGURE 5 is a vertical cross-sectional view showing the connectorelement formed in accordance with the invention with a threaded elementin place ready to be fastened.

FIGURE 6 is a vertical cross-sectional view showing the finishedconnector after the end of the connector element made in accordance withthe invention has been beaded over the flanged end of the threadedelement.

DETAILED DESCRIPTION OF THE INVENTION One of the objects of theinvention is to provide a novel connector element for rigid electricalconduits.

Still another object of the invention is to provide a novel method forforming a connector element having an internal shoulder.

A further object of the invention is to provide apparatus for forming aninternal shoulder in a hollow element in a high speed operation.

Other objects of the invention will become apparent from the followingdescription and the accompanying drawing.

In the drawing, the numeral 1 indicates a hollow, cylindrical metalelement which may be made of steel, brass, aluminum, or other metalwhich can be deformed but preferably C1010 or C1015 cold drawn steeltubing. In order to prepare the novel connector element of thisinvention the hollow cylindrical piece 1 is centered below stamping tool2 by means of supporting plate 3 and mandrel 4 fastened to the supportedplate by bolt 5. A cylindrical swaging or forging element 7 having anoutside diameter intermediate between the diameter of the outer Wall 9and the inner wall 11 of the cylindrical piece 1 is mounted on the lowerend of tool 2 by retainer 12 which in turn is fastened to tool 2 bymeans of bolt 13. As shown in FIGURE 3, retainer 12 is formed withshoulder 12' which abuts the end of element 7 and is tapered upwardlyfrom its leading surface and outwardly to a maximum diameter equal tothat of the diameter of the opening defined by shoulder 14 anddetermines the width of the shoulder. As shown in the drawing theexposed wall of the retainer element is frusto-conical. Although theretainer is shown with a slightly sloping wall it may be formed with awall substantially parallel to the wall of element 1. The retainer 12 isof sufiicient depth or thickness to confine the metal, forged from theinner wall of element 1, between the element Wall and the retainerduring the entire swaging or forging operation. By providing contiguouswall elements spaced apart a distance equal to the width of the desiredshoulder between Which the shoulder forms and is squeezed or com- 3pressed, a finished shoulder is formed in a single stroke or operation.As is evident from FIGURE 3, the shoulder is not squeezed against thebottom mandrel 4 and as a result the lower surface of the shoulder iscurved. By forcing tool 2 against the top end of piece 1, metal adjacentthe inner wall of the element is displaced and forced in the directionof mandrel 4. The diameter of the swaging tool 7 is preferably closer tothat of the inner diameter of the element 1 than the outer diameterthereof so that after the metal is displaced from the wall the thicknessof the portion of the Wall 16 above the shoulder 14 will be more thanhalf the thickness of the portion of the wall 17 below the shoulder. Theswaging operation is discontinued when the shoulder 14 has been formedat the desired locus. As an example, a connector element made of C1010or C1015 cold drawn, butt welded steel, having a length of 1 inches, anouter diameter of 1.125 inches and an inner diameter between .865 and.875 inch so that the wall thickness is between 0.13 and 0.125 inch, isswaged in accordance with my invention to form a shoulder at a depth of0.156 inch from the end to which the swaging element is applied, withthe shoulder extending radially inwardly a distance between 0.1675 and0.1685 inch from the inner wall from which the shoulder metal isdisplaced. The resulting connector element wall above the shoulder willhave its thickness reduced between 0.046 and 0.040 inch. The' thicknessof this portion of the wall was reduced by about /a.

As another example, an element made of C1010 or C1015 cold drawn, buttwelded steel tubing having a length of 1% inches, outside wall diameterof 1.312 inches and inside wall diameter between 1.075 and 1.085 inches,was swaged to form a shoulder at a distance of 0.133 inch from one end.The diameter of the opening defined by the resulting shoulder was about0.906 inch and the thickness of the wall from which metal was displacedwas about 0.058 inch. The thickness of the latter wall was reduced about48% As another example, C1010 or C1015 cold drawn, butt welded steeltubing having a length of 1 inches, outside wall diameter of 1.625inches and inside wall diameter of 1.340 to 1.350 inches, was swaged toform a shoulder at a distance of 0.172 inch from one end. The diameterof the opening defined by the resulting shoulder was about 1.188 inchesand the thickness of the wall from which metal was displaced was about0.087 inch. The thickness of the latter wall was reduced about 37.5%.

The thickness of the wall from which metal is displaced should not beless than about 0.1 to 0.15 inch since undesirable distortion of thetubular element may occur during the swaging operation if the wall istoo thin. On the other hand, the amount of metal swaged from theinterior of the tubular piece must be sufiicient to form a solid mass ofshoulder integral with the interior surface of the piece. We have foundthat by limiting the thickness swaged or displaced from the Wall toabout 0.04 to 0.06 inch excellent results are obtained with high speedproduction. It should be understood that tubular stock having a wallthickness greater than that of the aforesaid examples may be usedprovided the thickness of the metal swaged to form the shoulder is ofthe order of .04 to .06 inch.

The connector element after the shoulder has been formed bythe aforesaidswaging operation is shown in FIGURE 4. It will be noted that the upperface 19 of the shoulder 14 is smooth and flat, whereas the under face 21has a curved surface gradually increasing in thickness from the innercircular periphery to the line of juncture with the wall portion 17. Theinner wall 18, formed by removing metal to form the shoulder, is alsosmooth, as if it had been machined.

By carefully controlling the thickness of metal displaced from the innerwall of the element, the swaging operation can be performed without thenecessity of using a supporting or retaining die fitting closely aroundthe outer wall of the element which would ordinarily be required toprevent distortion of the element during the swaging operation. Whenusing a retaining die distortion of the element during the swagingoperation results in binding between the die and element and theattendant problem of freeing the two from each other. By reason of thefact that a retaining die is not used the swaging operation can beperformed rapidly since the problem of freeing the element from theretaining die is avoided.

The connector element, after the shoulder has been formed is designatedgenerally by the numeral 23. In making a finished connector, the element23 has a threaded hole 25 (FIGURES 5 and 6) formed in the wall below theshoulder 14 in order to enable a set screw to be threaded therein andscrewed against an electrical conduit (not shown) which is inserted intothe element 23. A threaded hollow element 27 having an outwardlyextending flange 29 the circumference of which is slightly less thanthat of the inner wall 22 is placed in the element 23 with the flangeresting on the shoulder 14. The upper end 15 of the element 23 is thenbeaded over the flange 29 as shown at 31 (FIGURE 6), thereby fasteningthe element 27 securely to the element 23 and forming a finishedconnector.

It will be apparent how the finished connector shown in FIGURE 6 isutilized. The threaded element23 is inserted in a hole in an electricalbox until the beaded end 31 abuts against the outside of the box and alock nut is then threaded on the element 27 on the inside of the box tohold the connector securely in the box.

Connector elements in accordance with the invention are produced onautomatic, intermittent high speed stamping presses. Speeds of 35 to 40units per minute can be made with each swaging tool. The speed ofproduction of connectors made in accordance with my invention has beenincreased ten-fold over the speed of production by methods heretoforeused, with a resulting significant reduction in cost. This has been madepossible by eliminating the use of an outside die thereby avoiding thedifficulty in removing the piece from the die after the swagingoperation. When an outside die is used, the connector element binds tothe die due to the slight expansion in circumference of the element inthe area of the swaging or forging operation.

Although specific examples have been given it will be understood thatconnectors of different sizes can be made in accordance with theinvention. The wall thickness of the connector element should besufficient to swage metal therefrom to form the shoulder and leavesufficient wall length and thickness to form a bead.

Although the invention has been described as applied to the formation ofshoulders in steel connector elements, it is applicable to formation ofshoulders in other types of hollow pieces made of sufliciently ductilematerial to be drawn or forged.

I claim:

1. The method of forming a shoulder interiorly of a hollow, open-endedelement having a wall thickness not less than about 0.1 inch and made ofmaterial sufficiently ductile to be forged, comprising centering andsupporting said element concentrically below a swaging tool by means ofa plate and mandrel at the lower end of said element, the outerperiphery of which tool corresponds to that of the periphery of theinner wall of said element but has a diameter approximately .08 to .12inch greater than that of said inner wall, forcing said tool downwardlyagainst the upper end of said element with sufficient force to displacemetal from the interior of said element while the outer wall of theupper end of said element is unconfined by a supporting die, providing aconfining wall adjacent the bottom of said tool, said confining wallbeing concentric with the inner Wall of said element and spacedtherefrom a distance equal to the width of the desired shoulder therebyto form an annular space between the inner Wall and confining wall,continuing to displace metal from said element into said annular spaceuntil the shoulder has attained the desired width and withdrawing thetool from the element.

2. The method in accordance with claim 1 in which the element is made ofsteel and has a wall thickness of approximately 0.1 to 0.15 inch.

3. The method in accordance with claim 2 in which the shoulder is formedwithout supporting the surface thereof opposite that contacted by theswaging tool.

4. Method in accordance with claim 1 in which the confining walladjacent the bottom of said tool is frustoconical in shape with the wallsloping outwardly from its leading end.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 6/1924 France.

France.

CHARLES W. LANHAM, Primary Examiner 15 E. M. COMBS, Assistant ExaminerU.S. Cl. X.R.

